For example, periodontal tissue is sequentially damaged from the edge of gums and alveolar bone is gradually lost as periodontitis proceeds, and thus so-called pyorrhea alveolaris that the tooth around the periodontitis is loose appears. As treatment for the pyorrhea alveolaris, a very loose tooth being hopeless of preservation is extracted, but a tooth being loose but hopeful of preservation is fixed together with an inconsiderably loose tooth adjacent thereto.
When a plurality of teeth adjacent to each other is fastened, a metal wire is generally used. In this method, the plurality of teeth to be fastened is wound with the metal wire while using the elasticity of the metal wire, and a load caused by the tensile and bend characteristics of the metal wire is applied to these teeth, so that the teeth can be fixed by this load.
However, the foregoing method has problems that man hours are needed in sequentially wounding and attaching the metal wire around the teeth, a patient always feels pain and his/her displeasure with the added load, and the metal wire stands out in front and looks ugly when opening his/her mouth.
Accordingly, there have recently been proposed methods of fixing a set of teeth using shape memory alloy. In these methods, a straightening member of a shape memory alloy wire previously undergoes heat treatment so that a shape in a parent phase can have a desired shape, i.e., a shape corresponding to an anatomically even set of teeth, and this straightening member is installed in accordance with the patient's set of teeth at low temperature and straightens the irregular teeth by returning to its original shape when warmed.
FIG. 1 shows a schematic view and a cross-section view of a conventional wire for straightening irregular teeth.
As shown in (a) of FIG. 1, a wire 10 for straightening irregular teeth looks similar to a general wire on the exterior. However, the wire 10 for straightening irregular teeth is internally different from the general wire, and therefore the shape and the manufacturing process thereof will be described in short with reference to (b) of FIG. 1.
(b) of FIG. 1 shows a cross-section taken from “A” in the wire 10 for straightening irregular teeth shown in (a) of FIG. 1.
Referring to (b) of FIG. 1, the conventional wire 10 for straightening irregular teeth includes a metal wire 11, and a Teflon coating film 13 formed on the surface of the metal wire 11. The metal wire 11 may be a general metal wire or a wire made of shape memory alloy. Further, the Teflon coating film 13 is coated on the metal wire 11 by various coating methods. The color of the Teflon coating film 13 is similar to the color of teeth.
As above, the conventional wire for straightening the irregular teeth is formed by coating the surface of the metal wire with the Teflon coating film in order to color the teeth. However, Teflon is being debated because of its toxic properties. A need for providing a wire for straightening irregular teeth, which is harmless to a human body, is urgent.